High power LED package with universal bonding pads and interconnect arrangement

ABSTRACT

LED packages are provided that can accommodate more than one type of LED. These packages include at least three bonding pads arranged such that two are appropriate for one type of LED, while another two are appropriate for another type of LED. Packages can include a thermally conductive layer on which the bonding pads and associated traces are disposed. The packages can also include electrical contacts on either of their top or bottom surfaces that are electrically coupled to the bonding pads by metallized vias or partial vias defined along edges or corners of the packages. Packages for multiple LEDs are also provided. These packages can enable the LEDs to be selectively operable.

CROSS-REFERENCE TO RELATED APPLICATIONS

The application claims the benefit of U.S. Provisional PatentApplication No. 60/623,266 entitled “1-5 Watt and Higher LED Packages,”U.S. Provisional Patent Application No. 60/623,171 entitled “3-10 Wattand Higher LED Packages,” and U.S. Provisional Patent Application No.60/623,260 entitled “5-15 Watt and Higher LED Packages,” each filed onOct. 29, 2004 and each incorporated herein by reference in its entirety.The application is related to U.S. patent application Ser. No.11/259,818 entitled “LED Package with Structure and Materials for HighHeat Dissipation,” and U.S. patent application Ser. No. 11/260,101entitled “Method of Manufacturing Ceramic LED Packages,” both filed oneven date herewith. The application is also related to U.S. patentapplication Ser. No. 11/036,559 filed on Jan. 13, 2005 and entitled“Light Emitting Device with a Thermal Insulating and Refractive IndexMatching Material,” which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates generally to light emitting diodes andmore particularly to packages for high-power LEDs.

2. Description of the Prior Art

A light emitting diode (LED) is a semiconductor device that produceslight when an electric current is passed therethrough. LEDs have manyadvantages over other lighting sources including compactness, very lowweight, inexpensive and simple manufacturing, freedom from burn-outproblems, high vibration resistance, and an ability to endure frequentrepetitive operations. In addition to having widespread applications forelectronic products as indicator lights and so forth, LEDs also havebecome an important alternative light source for various applicationswhere incandescent and fluorescent lamps have traditionallypredominated.

Using phosphors as light “converters,” LEDs can also serve to producewhite light. In a typical LED-based white light producing device, amonochromatic LED is encapsulated by a transparent material containingappropriate phosphors. In some systems, an LED that produces amonochromatic visible light is encapsulated by a material containing acompensatory phosphor. The wavelength(s) of the light emitted from thecompensatory phosphor is compensatory to the wavelength of the lightemitted by the LED such that the wavelengths from the LED and thecompensatory phosphor mix together to produce white light. For instance,a blue LED-based white light source produces white light by using a bluelight LED and a phosphor that emits a yellowish light when excited bythe blue light emitted from the LED. In these devices the amount of thephosphor in the transparent material is carefully controlled such thatonly a fraction of the blue light is absorbed by the phosphor while theremainder passes unabsorbed. The yellowish light and the unabsorbed bluelight mix to produce white light. Another exemplary scheme uses an LEDthat produces light outside of the visible spectrum, such as ultraviolet(UV) light, together with a mixture of phosphors capable of producingeither red, green, or blue light when excited. In this scheme, the lightemitted by the LED only serves to excite the phosphors and does notcontribute to the final color balance.

Recent advances in semiconductor technology have made it possible tomanufacture high-power LEDs that produce light at selected wavelengthsacross the visible spectrum (400-700 nm). Such high-power LEDs can havereliability and cost advantages over existing technologies such asincandescent lamps, arc lamps, and fluorescent lamps in many lightingapplications. High-power LEDs also offer advantages for design of nextgeneration color display technologies such as active matrix thin filmtransistor liquid crystal displays (TFTLCDs) in applications such asconsumer computer and television monitors, projection TVs, and largeadvertising displays.

Although high-power LED devices have been manufactured, their widespreaduse has been limited because of a lack of suitable packages for theLEDs. Current LED packages cannot handle the high-power density of LEDchips. In particular, prior art packages provide inadequate heatdissipation away from the LED dies. Inadequate heat dissipation limitsthe minimum size of the package and therefore the density of LEDs perunit area in the device. One measure of how efficiently a packagedissipates heat is the temperature rise across the package for a giveninput electrical power. This measure is generally in the range of 15 to20 degrees centigrade per watt (° C./W) from the junction to the case incurrent LED packages, usually too high to provide adequate heatdissipation for an LED package having a power higher than 1 watt.

Without sufficient heat dissipation, devices incorporating high-poweredLEDs can run very hot. Light output, LED efficiency, and LED life, areeach dependent on the LED die junction temperature. Inadequate heatdissipation will cause the LED Die to operate at a higher temperatureand therefore limits the performance of the LED die when the LED die iscapable of operating at a power level exceeding the limits of thepackage. Insufficient heat dissipation by an LED package can cause theLED device to fail at an early stage or render it too hot to use safely.

Even under less severe conditions, inadequate heat conduction for an LEDpackage may result in poor thermal stability of the phosphors, as wellas encapsulation and lens materials, in those devices that employphosphors. Specifically, exposure to high temperatures for extendedperiods tends to alter the chemical and physical properties of suchphosphors, encapsulation, and lens materials, causing performancedeterioration. For instance, the light conversion efficiency can declineand the wavelength of output light can shift, both altering the balanceof the light mixture and potentially diminishing the intensity of theoverall output. For example, currently available phosphors are oftenbased on oxide or sulfide host lattices including certain rare earthions. Under prolonged high temperature conditions, these latticesdecompose and change their optical behavior. Other problems commonlyfound with LED-based white light sources are transient color changes anduneven color distributions, both caused by temperature gradients in thephosphor-containing material and degradation of the encapsulation andlens materials. Such behaviors often create an unsatisfactoryillumination. The above-mentioned thermal problems worsen withincreasing temperature and therefore are particularly severe for devicesthat incorporate high-power LEDs with phosphors.

Attempts have been made in current LED packages to alleviate the aboveproblem. One example is to directly attach an LED die to a top surfaceof a metal heat slug such as a copper plate. The copper plate serves tospread the heat and to make electrical connections with the LED die.This design limits the selection of materials for the heat slug becausethe design relies at least partially on the conductive nature of thecopper for making the conductive contacts between the LED die and thetop surface of the copper heat slug. The use of copper heat slugs alsohas other limitations, such as a substantial mismatch between thecoefficients of thermal expansion (CTE) of the LED die material and thecopper onto which the LED die is attached. A large CTE mismatch cancreate high stresses upon heating a cooling at bonded interfaces. Cracksthat form at these interfaces then render the LED package unreliable. Inaddition, the above design is relatively expensive and difficult tomanufacture.

Given the importance of LEDs as light sources, particularly high-powerLEDs, there is a need for improved LED packaging methods and materialsto alleviate the above-identified problems by providing better thermalperformance (e.g., improved thermal resistance from junction to case)and higher reliabilities (e.g., lower stresses in packaging materials).Such packaging methods and materials will allow LEDs to produce higheroptical performance (Lumens/package) from a smaller package or footprint(Lumens/area), which are critical for many light source applications.

SUMMARY

The present disclosure addresses the above problems by providing apackage for an LED. An exemplary embodiment of the package is auniversal LED package for accommodating different LED types, such asvertical, flip-chip, and planar LEDs from a variety of manufacturers. Inthis embodiment the universal LED package comprises a body including topand bottom surfaces, a cavity extending from the top surface towards thebottom surface and having a floor that is substantially parallel to thebottom surface, and first, second, and third electrically conductivebonding pads disposed on the floor of the cavity. The first and secondbonding pads are arranged to provide electrical contacts for a first LEDtype, and the first and third bonding pads are arranged to provideelectrical contacts for a second LED type. In some embodiments, one ofthe electrically conductive bonding pads is centrally located on thefloor within the cavity.

In further embodiments, the package also comprises an electrical path,including such features as traces and vias, connecting the first pad toan exterior contact disposed, for example, on a top or bottom surface ofthe body. The electrical path can include a metallized partial viadisposed on an edge or corner of the body.

Another exemplary embodiment is an LED package comprising a bodyincluding top and bottom surfaces, a cavity extending from the topsurface towards the bottom surface and having a floor that issubstantially parallel to the bottom surface, and first and secondelectrically conductive bonding pads disposed on the floor of thecavity. The first and second bonding pads are configured to completelycover the floor of the cavity except for a narrow gap therebetween.Since the bonding pads substantially cover the floor of the cavity, thefloor is made to be highly reflective. The body further includes, insome of these embodiments, a top body layer disposed above the ceramiclayer. In these embodiments the cavity is disposed through the top bodylayer. Also, in some of these embodiments the top body layer alsocomprises a ceramic.

Yet another exemplary embodiment is an LED package for multiple LEDs.This package comprises a body including top and bottom surfaces, acavity extending from the top surface towards the bottom surface andhaving a floor that is substantially parallel to the bottom surface, athermally conducting material disposed between the floor and the bottomsurface, a plurality of LED bonding pads disposed on the floor, and aplurality of electrical bonding pads disposed on the floor proximate tothe LED bonding pads and in electrical communication with a plurality ofelectrical contacts disposed on a surface of the body. In various ofthese embodiments, the thermally conducting material can comprise aceramic, and the plurality of LED bonding pads are non-electricallyconductive. The plurality of electrical contacts can also be disposed onthe top or bottom surface of the body, and the plurality of electricalbonding pads can be in electrical communication with the plurality ofelectrical contacts through a plurality of vias, which can be partialvias. The package can also comprise an ESD protection device coupledbetween two of the plurality of electrical bonding pads.

Light emitting devices are also provided that comprise a package and oneor more LEDs. In one such embodiment, the package includes top andbottom surfaces, a cavity extending from the top surface towards thebottom surface and having a floor that is substantially parallel to thebottom surface, a thermally conducting material disposed between thefloor and the bottom surface, a plurality of LED bonding pads disposedon the floor, and a plurality of electrical bonding pads disposed on thefloor proximate to the LED bonding pads and in electrical communicationwith a plurality of electrical contacts disposed on a surface of thebody. In the embodiment a plurality of LED dies disposed on theplurality of LED bonding pads and electrically coupled to the pluralityof electrical bonding pads. In various further embodiments the LED diesare electrically connected in series or selectively operable. Theplurality of LED bonding pads can be electrically conductive. The lightemitting device can also comprise a luminescent layer disposed over theLED dies, and a thermal insulation layer between the luminescent layerand the LED dies.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an LED die bonded to an exemplary LEDpackage according to an embodiment of the present disclosure.

FIG. 2 is a cross-sectional view of an exemplary embodiment of the LEDpackage of the present disclosure.

FIG. 3 is a top view of an exemplary LED package of the presentdisclosure.

FIGS. 4A and 4B are exemplary metallization patterns for a top surfaceof a thermally conducting layer of an LED package according toembodiments of the present disclosure.

FIG. 5 is an exemplary metallization pattern for the bottom surface of athermally conducting layer of an LED package according to an embodimentof the present disclosure.

FIGS. 6A-6C are cross-sectional views of several exemplary embodimentsof an LED package of the present disclosure.

FIG. 7 is a top view of an LED package in accordance with anotherembodiment of the present disclosure.

FIG. 8 is a top view of a plurality of LED packages manufactured inparallel during an exemplary embodiment of a fabrication process.

FIG. 9 is another exemplary metallization pattern for a top surface of athermally conducting layer of an LED package according to anotherembodiment of the present disclosure.

FIG. 10 is another exemplary metallization pattern for a bottom surfaceof a thermally conducting layer of an LED package according to anotherembodiment of the present disclosure.

FIG. 11 is a top view of an LED package showing an exemplarymetallization pattern on a top surface of the body of the package,according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

1. An Overview

The present disclosure provides LED packages with structures andmaterials that provide higher heat dissipation than presently available.A further benefit of the present invention is improved matching of thecoefficients of thermal expansion (CTEs) of the LED dies and thematerials to which they are bonded for higher reliability. Due to theimproved heat conduction, the packages of the present invention allowhigh-power LEDs to operate at full capacity. Improved heat conductionalso allows for both smaller packages and devices within which packagesare placed more closely together.

One measure of how efficiently a package dissipates heat is thetemperature rise across the package. Using this measure, in currenthigh-power LED packages the thermal resistance from the junction to thecase is generally in the range of 15 to 20° C./W. By comparison, anexemplary embodiment of the present disclosure has a lower thermalresistance of only about 6° C./W or 3° C./W for a four LED dice package.Therefore, the present disclosure enables LED devices for newapplications in both high temperature environments (such as in anautomobile engine compartment) and also in environments that cannotaccommodate high temperature components (such as a dental curing lightfor use in a patient's mouth).

Accordingly, exemplary packages for high-power LEDs according to thepresent disclosure have the following features: 1) They offer higherperformance by enabling 50% or greater luminosity per LED die ascompared to prior art packages; 2) they provide a high thermalconductivity path to conduct heat away from LED dies; 3) they redirectlight emitted at low solid angles (tangential light) into directionsmore nearly perpendicular to the surface of the LED die; and 4) theyprovide a material layer, for bonding to the LED die, having a CTE thatis closely matched to the CTE of the LED die to minimize interfacialstresses and improve reliability.

The present disclosure provides embodiments for a package for a singlehigh-power LED die in the 1 to 7 watt output power range that providesthe desirable features discussed above. The present disclosure alsoprovides embodiments to stabilize the wavelength (i.e., color) of LEDdies. In the case of white LED applications, the present disclosureprovides embodiments for improving white light LED efficiency.

The present disclosure also provides embodiments for a package formultiple high-power LED dies with a combined output in the 1 to 15 wattoutput power range. These packages have very small form factors and canbe fabricated at low cost. The small form factors enable the design oflight source optics with more compact sizes. Therefore, the presentinvention enables a new class of high-power LED-based light source anddisplay applications to emerge.

The packages of the present invention can be used with LED devices thatoperate over the range of wavelengths from ultraviolet (UV) to Infrared(IR) which covers the range from 200 to 2000 nanometers. Further,packages of the present invention can include bonding pads configured toaccommodate any of a number of different LED die designs that arepresently available in the market. The present disclosure, in someembodiments, also provides a versatile package design whereby thethermal and electrical paths are separated. In this way, the package canbe attached to a heat sink of a circuit board using either a thermallyand electrically conductive epoxy or solder, or a thermally conductiveand electrically non-conductive epoxy.

2. Exemplary Embodiments

FIG. 1 is a perspective view of an exemplary LED package 100 accordingto an embodiment of the invention. To form a light emitted device, a die110 is bonded to the LED package 100 as shown. The LED package 100comprises a body 120 having a cavity 130 extending downward from a topsurface 140 thereof. The cavity 130 includes a floor 150 for bonding tothe LED die 110. In some embodiments, the LED package 100 has a squarefootprint enabling multiple light emitting devices to be denselyarranged in a square array. The LED package 100 is intended primarilyfor LED dies that produce 1-5 watts of power, but is not limitedthereto.

In the embodiment shown in FIG. 1, a sidewall 160 of the cavity 130 isinclined at an angle so that the cavity 130 takes the shape of aninverted and truncated cone. The sidewall can also be vertical, ornearly so. In some embodiments the sidewall 160 of the cavity 130 isinclined at a 45° angle. Preferably, the sidewall 160 is highlyreflective at a wavelength emitted by the LED die 110. This can beachieved, for example, with a coating of a highly reflective materialsuch as silver, though other materials can be used, depending on thewavelength of the light produced by the LED die 110. Thus, the sidewall160 can serve to redirect light emitted from the edges of the LED die110. The light from the edges of the LED die 110 is redirected in adirection perpendicular to a top surface of the LED die 110 so that thelight emitted from the side surfaces of the LED die 110 adds to thelight emitted from the top surface of the LED die 110. In otherembodiments the sidewall 160 takes a parabolic shape to better focus theredirected light.

FIG. 2 is a cross-sectional view of one exemplary embodiment of an LEDpackage 200 of the present disclosure. It can be seen from FIG. 2 thatthe LED package 200 comprises three layers (embodiments with four layersare described elsewhere herein) designated from top to bottom as a topbody layer 210, an intermediate body layer 220 and a thermal conductionlayer 230. The thermal conduction layer 230 has a bottom surface 235. AnLED die 240 can be bonded to a top surface of thermal conduction layer230 within a cavity 250 formed through layers 210 and 220. A thicknessof intermediate body layer 220 is designed to be approximately the sameas a thickness of a die attach layer 245 that bonds the LED die 240 tothe thermal conduction layer 230. Also, in some embodiments ametallization layer on a sidewall 255 of the top body layer 210 extendsfrom a top rim 260 at a top surface 280 of the top layer 210 to a bottomrim 270 near a bottom surface of the top body layer 210.

FIG. 3 is a top view of the exemplary LED package 200 of FIG. 2. The toprim 260 and the bottom rim 270 correspond to the outer diameter and theinner diameter of the cavity 250 and are represented by two circles 260and 270, respectively. It can be seen that the LED die 240 is positionedwithin the inner diameter 270. This embodiment also includes partialvias 290, 292, 294, and 296, one at each of the four corners of the LEDpackage 200. As used herein, a partial via is a via defined at an edgeor a corner of the LED package 200 and therefore appears as ahalf-circle or quarter-circle. The partial vias 290, 292, 294, and 296are metallized, in some embodiments, to serve as electrical pathsbetween electrical contacts and traces on the surfaces of the layers210, 220, and 230. It will be appreciated that the partial vias 290,292, 294, and 296 are conveniently formed and metallized by fabricationmethods discussed below in connection with FIG. 8, however, standard(e.g. full-circle) metallized vias defined through the layers 210, 220,and 230 can also be employed for making such electrical connections.

The thermal conduction layer 230 includes a thermally conductivematerial, which preferably has a thermal conductivity greater than about14 W/m° K., and more preferably has a thermal conductivity greater than150 W/m° K. Depending on applications, power density, desired packagesize and thickness of the several layers, a variety of thermallyconductive materials can be used to form the thermal conduction layer230. Such materials include, but are not limited to, aluminum nitride(AlN), alumina (Al₂O₃), Alloy 42, copper (Cu), copper-tungsten (Cu/W)alloy, aluminum silicon carbide, diamond, graphite, and beryllium oxide.In addition to thermal conductivity, the coefficient of thermalexpansion (CTE), the fracture toughness, Young's modulus, and cost areother parameters to be considered in selecting the material for thethermal conduction layer 230.

Matching the CTE of the thermally conductive material with that of theLED die reduces interfacial stresses and therefore improves reliability.Preferably, the CTE of the thermally conductive material should be lessthan 15 parts per million per degree centigrade (ppm/° C.) in order tomore closely match the CTE of typical LED die materials such as silicon.The mismatch in the CTEs between the LED package and the LED dieaccording to embodiments of the present disclosure is about 4.7:3,whereas for prior art packages the best ratios are about 17:3. Improvedheat dissipation allows packages of the present disclosure to have asmaller footprint and to be thinner than prior art packages. Anexemplary embodiment of the present disclosure has dimensions of 4.4mm×4.4 mm×0.9 mm vs. prior art packages that measure 14 mm×7 mm×2.5 mm.

The thermal conduction layer 230, with the help of layers 210 and 220 insome embodiments, dissipates much of the heat generated by the LED 240.For applications that demand the highest thermal dissipationcapabilities, each of the three layers 210, 220, and 230 compriseceramic AlN. AlN is desirable because it combines high thermalconductivity with a CTE that is very similar to that of LED substratematerials, such as SiC, sapphire, or silicon, the material from whichsolid-state LEDs are most frequently fabricated. However, Al₂O₃ can alsobe used for these layers for other applications. For some applications,thermal conduction layer 230 is made from either AlN or Al₂O₃ whilelayers 210 and 220 are made of other suitable materials includingplastics and metals such as copper, aluminum, and Alloy 42. For someapplications it is desirable to use the thermal conduction layer 230 asthe primary thermal conduction path away from the LED die 240 in orderto prevent heat from being directed towards the top of the package 200.For example, it may be desirable to keep the top of the light emittingdevice cool to the touch.

It will be appreciated that the package 200 does not need to be formedfrom three layers as illustrated by FIG. 2; more or fewer layers alsocan be used. For example, an embodiment with four layers is alsodescribed herein. Ceramic processing techniques can also be used to formthe body as an integral unit. However, a layered configuration isdesirable for the ease of fabrication. For some applications withsecondary lenses, layers 210 and 220 are optional.

It will also be appreciated that heat produced by the LED die 240 isdissipated from the package 200 primarily through the thermal conductionlayer 230. Consequently, layer 230 preferably has a thickness that isoptimized for thermal conductivity therethrough. It has been found thatfor a given material, the thermal conductivity decreases if layer 230 iseither too thin or too thick and, accordingly, there is an optimalthickness for optimal thermal conductivity. In the embodiment where AlNceramic is used for a thermal conduction layer 230, the optimalthickness of layer 230 is in a range of 0.2 mm to 0.4 mm, and ideallyabout 0.3 mm.

It will be appreciated that the LED package 200 may be further attachedto a heat sink (not shown) along the bottom surface 235. In addition, tooptimize heat dissipation from the package 200 to the heat sink, the dieattach layer 245 is preferably also thermally conductive. In the presentdisclosure, for a thin layer to be characterized as being thermallyconductive, the material of the layer should have a thermal conductivityof at least 0.5 W/m° K., and ideally about 50 W/m° K.

In some embodiments, the thermal conductivity of the die attach layer245 is desirably at least 1 W/m° K. The die attach layer 245 cancomprise, for example, an electrically conductive epoxy, a solder, athermally conductive and electrically non-conductive epoxy, or anano-carbon-fiber filled adhesive. In some embodiments as discussedbelow, where the LED die 240 needs to make an electrical connection withthe thermal conduction layer 230 through a central pad, the die attachlayer 245 is also electrically conductive. In this disclosure, a thinlayer material is considered to be electrically conductive if it has avolume resistivity less than 1×10⁻² ohm-meter. A material for anelectrically conductive die attach layer 245 desirably has a volumeresistivity less than 1×10⁻⁴ ohm-meter.

The thermal conduction layer 230, in accordance with the presentdisclosure, may be either electrically conductive or electricallynonconductive. As described below, where the thermal conduction layer230 is electrically nonconductive, the present disclosure uses ametallization pattern for the top surface of the thermal conductionlayer 230 to provide necessary electrical contacts. This unique designmakes it possible to fabricate the thermal conduction layer 230 fromthermally conductive materials that are not electrically conductive,such as ceramics. Electrically nonconductive materials haveconventionally been considered unsuitable for making heat slugs.

FIG. 4A illustrates an exemplary metallization pattern for the topsurface 400 of thermal conduction layer 230 of the LED package 200 ofFIGs. 2 and 3. It can be seen that a generally square central pad 410 isconnected by a trace 420 to one of the four partial vias (290, 292, 294,and 296), and partial via 294 particularly in FIG. 4A. Nickel andtungsten are exemplary metals for the metallization. The bottom surfaceof the LED die 240 is bonded, for example by solder, a thermally andelectrically conductive adhesive, or a thermally conductive andelectrically non-conductive adhesive, to the central pad 410.

The central pad 410 is surrounded on three sides by three bonding pads430, 440, and 460, each connected to one of the remaining three partialvias 290, 292, and 296. An electrical contact (not shown) on the topsurface of the LED die 240 is wire bonded to one of these three bondingpads 430, 440, and 460 where exposed on the floor of the cavity250.(i.e., within the circle 270). The four partial vias 290, 292, 294,and 296 connect the bonding pads 430, 440, and 460 and the central pad410 to external electrical contacts (not shown) on either the top oflayer 210 or the bottom of layer 230, or both. These external electricalcontacts provide leads to a power source on a circuit board. It can beseen from FIGs. 2-4 that after the package 200 is fully assembled mostof the metallization pattern shown in FIG. 4A is sandwiched betweenlayers 230 and 220 and hidden from view.

In the embodiment shown above in FIG. 4A, the central pad 410 servesboth as an electrical connector and a thermal bonding pad between theLED die 240 and the top surface 400 of the thermal conduction layer 230.To facilitate electrical connection, the LED die 240 may be eitherdirectly bonded to the central pad 410 or attached thereto using anelectrically conductive adhesive. In this disclosure, an adhesive isconsidered to be electrically conductive if it has a volume resistivityless than 1×10-2 ohm-meter. For better performance, an electricallyconductive adhesive desirably should have a volume resistivity less than1×10-4ohm-meter. It should be understood, however, that in someembodiments the central pad 410 serves as a thermal bonding pad but notas an electrical connector, as described elsewhere herein. In suchembodiments, the central pad 410 is not connected to one of the partialvias 290, 292, 294, and 296. Instead, all partial vias 290, 292 296, and294 are connected to a respective pad (such as the bonding pads 430,440, and 460 and the central pad 410).

It will be appreciated that the arrangement of the bonding pads 430,440, and 460 around the central pad 410 allows the package 200 to beused with different types of LED dies 240 that require different bondingpad arrangements. For example, a first type of LED die 240 may makeelectrical connections to the central pad 410 and bonding pad 430, whilea second type of LED die 240 may make electrical connections to thecentral pad 410 and bonding pad 440. In those embodiments in which thecentral pad 410 is a thermal bonding pad but not an electrical bondingpad, a third type of LED die 240 may make electrical connections tobonding pads 430 and 460, for example. It will be appreciated,therefore, that different types of LED dies 240 can utilize differentsubsets of the bonding pads. Thus, the package 200 is said to beuniversal to more than one type of LED die 240.

FIG. 4B illustrates another exemplary metallization pattern for the topsurface 400 of thermal conduction layer 230 of the LED package 200 ofFIGs. 2 and 3. In this embodiment a first pad 470 is connected to twopartial vias 292, 294, and a second pad 480 is connected to the othertwo partial vias 290, 296. An exemplary spacing between the first andsecond pads 470 and 480 is 0.10 mm. Nickel, tungsten, and silver areexemplary metals for the metallization. In some embodiments, silver iscoated over another metal, such as nickel. Line 490 indicates where thebottom surface of the LED die 240 is bonded to the first pad 470. Onebenefit of the exemplary metallization pattern of FIG. 4B, compared tothe metallization pattern shown in FIG. 4A, is that a greater area ofthe floor of the cavity within the inner diameter 270 is metallized,which serves to reflect a greater amount of light upward and out of thepackage.

FIG. 5 illustrates an exemplary metallization pattern for the bottomsurface 235 of the thermal conduction layer 230. In this embodiment, acentrally located pad 510 provides a thermal path from the bottomsurface 235 of thermal conduction layer 230 to a substrate (not shown)to which the package 200 is attached. The substrate can include a heatsink. The pad 510 is circular or square in some embodiments, but is notlimited to any particular shape.

Each of the four partial vias 290, 292, 294, and 296 at the corners ofthe package 200 connect to one of the separate semi-circular electricalcontacts 530, 540, 550, and 560, respectively. One of the foursemi-circular electrical contacts, 550 in this particular embodiment, isconnected through one of the four partial vias (294 in this case) andtrace 420, as shown in FIG. 4A, to the central pad 410, while the otherthree semi-circular electrical contacts (530, 540, and 560 in thisembodiment) connect to the three bonding pads 430, 440, and 460,respectively. Trace 420 and central pad 410 are shown in dotted line inFIG. 5 to indicate that they are on the opposite (top) surface of thethermal conduction layer 230. Thus, when attached to the substrate, thecentrally located pad 510 is soldered (or otherwise bonded, such as witha thermally conductive epoxy) to the substrate for heat dissipation andtwo of the four semi- circular electrical contacts 530, 540, 550, and560 are connected to electrical contacts on the substrate to provide anelectrical path through the LED package 200 and to the LED die 240. Oneof the two semi-circular electrical contacts (550 in this embodiment)connects through the central pad 410 to the bottom of the LED die 240,while the other (any one of 530, 540, and 560) is connected through itsrespective side bonding pad (430, 440, and 460) to the top of the LEDdie 240 by a wire bond (not shown). The particular semi-circularelectrical contact 530, 540, or 560 that is used to connect to the LEDdie 240 is determined according to the characteristics and therequirements of the particular LED die 240.

It will be understood that by having an arrangement of several bondingpads in a number of different locations enables the same package to beused with different LED designs. Thus, an LED from one manufacturer maybe bonded to one set of bonding pads while an LED from anothermanufacturer may be bonded to another set of bonding pads. In thisrespect the package is universal to different LEDs from differentsources. Further still, the design of the package of the presentinvention allows for flexible and simple processes for attaching LEDs tothe packages.

In alternative embodiments, the top surface 280 of the top body layer210 has a metallization pattern to provide electrical contacts ratherthan the bottom surface of the thermal conduction layer 230. Each of thepartial vias 290, 292, 294, and 296 at the corners and sides of the LEDpackage 200 connect to a separate electrical contact on the top surface140 of the top body layer 210. In these embodiments wire bonds to theelectrical contacts on the top surface or 140 of the top body layer 210connect the LED package 200 to a power source or a circuit board.Locating the electrical contacts on the top of the package 200 ratherthan the bottom provides a greater area of contact between the bottomsurface 235 and the substrate for even greater heat dissipation. The LEDpackage 200 in these embodiments can be bonded to a substrate, forexample, by solder or thermally conductive epoxy. The bond does not haveto be electrically conductive.

It will be appreciated that the packages of the present disclosureprovide improved heat dissipation in several ways, some of which arelisted as follows. In some embodiments, the use of a material havingsuperior thermal conductivity for the thermal conduction layer 230improves heat dissipation. In other embodiments, the accommodation foran electrically nonconductive material for thermal conducting makes itpossible to use unconventional thermally conductive materials, forexample AlN ceramic, to form the thermally conducting layer. In otherembodiments, optimizing the thickness of the thermal the conductinglayer 230 further improves heat dissipation. In still other embodiments,providing a large area of contact between the bottom surface 235 ofthermal conduction layer 230 and the substrate to which it attaches canfurther improve heat dissipation. In some embodiments, the packages ofthe present disclosure also direct a greater percentage of light out ofthe package, both reducing the heating of the package from absorbedlight and increasing the light production efficiency.

Because of the improved heat dissipation, exemplary packages accordingto the present disclosure exhibit thermal resistances of about 6° C./Wat an output greater than 1 watt per package. Exemplary packagesaccording to the present disclosure with four LED dice exhibit a thermalresistance of 3° C./W, with outline dimensions of 7 mm×7 mm×1 mm. Thepresent disclosure also makes highly compact LED packaging possible. Insome exemplary packages, the square LED package has a width and lengthof about 4.4 mm and a thickness of about 1 mm (with thicknesses of about0.5 mm, 0.1 mm and 0.3 mm for the top body layer, the intermediate bodylayer and the thermally conducting layer, respectively). The presentdisclosure therefore enables high-power LEDs to be used inhigher-temperature environments, such as in automotive enginecompartments, as well as in applications where high-temperaturecomponents cannot be tolerated, such as in dental applications, forexample, in an illumination device used to cure dental cements.

The features disclosed in the present disclosure can be combined withother techniques of LED packaging. For example, the package of thepresent disclosure can further use encapsulating techniques as describedin the U.S. patent application Ser. No. 11/036,559, entitled “LightEmitting Device with a Thermal Insulating and Refractive Index MatchingMaterial,” filed on Jan. 13, 2005, which is incorporated by referenceherein.

FIG. 6A is a cross-sectional view of another exemplary embodiment of theLED package of the present disclosure. From top to bottom, the LEDpackage 600 comprises layers 610, 620, and 630. Similar to the LEDpackage 200 of FIG. 2, layer 610 is a top body layer, layer 620 is anintermediate body layer, and layer 630 is a thermal conducting layer. AnLED 640 mounted to a top surface of thermal conducting layer 630 throughan LED die attach layer 645. A thermal insulation layer 650 and aluminescent layer 655 are placed in a tapered cavity having the shape ofan inverted cone. The cavity has a side wall extending from a top rim660 to a bottom rim 670. The LED package 600 also has an auxiliarymember 680 enclosing the package from the top. The auxiliary member 680is optional and can be, for example, an optical lens for focusing thelight emitted from the LED package 600. The auxiliary member 680 canalso serve as a protective capping layer.

It can be seen that the thermal insulation layer 650 is disposed betweenthe luminescent layer 655 and a top surface of the LED die 640. Thethermal insulation layer 650 at least partially protects the luminescentmaterial in the luminescent layer 655 from the heat produced by the LEDdie 640, thus better maintaining thermal properties, such as lightconversion efficiency and output wavelength, at or near optimal valuesfar longer than under the prior art. The thermal insulating material ofthermal insulation layer 650 can also be a material with an index ofrefraction chosen to closely match that of the material of the LED die640.

The use of a thermal insulating material to protect the luminescentmaterial within the encapsulant member from the heat produced by the LEDis made particularly effective when applied in the LED packages of thepresent disclosure. It will be appreciated that prior art light emittingdevices do not include thermal insulation to protect phosphors from theheat generated by the LEDs because heat dissipation has been anoverriding concern in such devices. Put another way, designers of priorart light emitting devices have sought to dissipate as much heat aspossible through the phosphor-containing layers (e.g., luminescent layer655) because to do otherwise would require too much heat dissipationthrough the remainder of the light emitting device. However, where thethermally conducting layer 630 provides sufficient heat conduction, itis no longer necessary to conduct heat through the phosphor-containingluminescent layer 655, and thermal insulation can be introduced toshield the luminescent materials.

The thermal insulation layer 650 is preferably transparent, or nearlyso, to the light emitted from the LED die 640. The thermal insulatingmaterial is therefore preferably transparent to at least one wavelengthemitted by the LED die 640. The wavelengths emitted by various availableLEDs extend over a wide spectrum, including both visible and invisiblelight, depending on the type of the LED. The wavelengths of common LEDsis generally in a range of about 200 nm-2000 nm, namely from theinfrared to the ultraviolet.

In order to effectively thermally insulate the luminescent layer 655,the thermal insulating material of the thermal insulation layer 650should have a low thermal conductivity, desirably with a thermalconductivity of no more than 0.5 watt per meter per degree Kelvin (W/m°K.), and more desirably with a thermal conductivity of no more than 0.15W/m° K. The thermal insulating material for the thermal insulation layer650 desirably also has high heat resistance, preferably with a glasstransition temperature, T_(g), above 170° C., and more preferably aglass transition temperature above 250° C. Furthermore, in order to havegood thermal compatibility and mechanical compatibility between thethermal insulation layer 650 and other components, especially the LEDdie 640, which are typically semiconductor materials, the thermalinsulating material desirably has a coefficient of thermal expansion nogreater than 100 ppm/° C., and more desirably a coefficient of thermalexpansion no greater than 30 ppm/° C.

Luminescent materials suitable for the present invention include bothfluorescent materials (phosphors) and phosphorescent materials.Phosphors are particularly useful for LED-based white light sources.Common phosphors for these purposes include Yttrium Aluminum Garnet(YAG) materials, Terbium Aluminum Garnet (TAG) materials,ZnSeS+materials, and Silicon Aluminum Oxynitride (SiAlON) materials(such as α-SiAlON).

The present invention also provides a light emitting device comprising apackage of the invention configured with an LED die and a luminescentmaterial. In one embodiment, light emitting device produces white lightbased on a monochromatic LED. This can be done, for example, by using avisible light LED and a compensatory phosphor, or by using an invisiblelight LED together with RGB phosphors. For instance, a blue LED-basedwhite light source produces white light by using a blue light LED and aphosphor that produces a yellowish light.

FIGS. 6B and 6C show cross-sections of additional embodiments of the LEDpackage 600. In FIG. 6B the top body layer 610 includes a circular notch685 to receive a lens 690. The lens 690 can be glass or plastic, forexample. The notch 685 beneficially provides a guide that centers thelens 690 over the LED die 640 during assembly. In some of theseembodiments, the top body layer 610 comprises a metal such as acopper-tungsten (Cu/W) alloy. The tapered cavity and the notch 685, insome of these embodiments, are formed by a stamping operation. Infurther embodiments, the intermediate body layer 620 and the thermalconducting layer 630 are also made of alumina.

In FIG. 6C the LED package 600 comprises an alignment layer 695 placedabove the top body layer 610. A circular aperture in the alignment layer695 creates essentially the same guide for the lens 690 as describedabove with respect to FIG. 6B. The alignment layer 695 can include, forexample, metal or ceramic. In those embodiments in which layers 610,620, and 630 include AlN, the alignment layer 695 can also include AlN.

The LED package of the present invention, in some embodiments, cansupport multiple LED dies within a single package to further increasethe output level and density. FIG. 7 is a top view of an LED package 700in accordance with another embodiment of the present disclosure. The LEDpackage 700 is similar to the LED package 200 in FIGS. 2-5, except thatthe LED package 700 contains multiple LEDs (710A, 710B, 710C, and 710D)instead of a single LED. The top view of the LED package 700 shows thecavity 730, the top surface 740, the outer diameter 760 and the innerdiameter 770 of the cavity 730, and the four partial vias 790, 792, 794,and 796. In the particular embodiment shown in FIG. 7, the LED package700 includes four LEDs 710A, 710B, 710C, and 710D, although in principleany other number of LEDs may be arranged in a package of the presentinvention. The four LEDs 710A, 710B, 710C, and 710D can be the same ordifferent, and in some embodiments are independently operable. Forexample, the multiple LEDs (710A, 710B, 710C and 710D) may beselectively operable and may be operable in any combination. The LEDpackage 700 is intended to provide an LED package capable of producingan output of 1-15 watts with a thermal resistance of 3° C./W, but is notlimited thereto.

FIG. 9 illustrates an exemplary metallization pattern for a top surfaceof a thermal conduction layer 900 of the LED package 700 of FIG. 7. Itcan be seen that four generally square central pads 905, 910, 915, and920 are arranged in a square array. The LEDs 710A-D (FIG. 7) mount tothe central pads 905, 910, 915, and 920. The central pads 905, 910, 915,and 920 are surrounded by five bonding pads 925, 930, 935, 940, and 945.In this embodiment, each of the central pads 905, 910, 915, and 920 isconnected by a trace to one of the bonding pads 925, 930, 935, and 940and to one metallized partial via 950, 955, 960, and 965. The fifthbonding pad 945 is connected by a trace to a fifth partial via 970. Thebottom surface of the LED die 240 is bonded, for example by solder, or athermally and electrically conductive adhesive.

In one embodiment, LED 710C (FIG. 7) is disposed on central pad 915 anda contact on the top surface of the LED 710C is wire bonded to bondingpad 945. Likewise, LED 710D (FIG. 7) is disposed on central pad 920 anda contact on the top surface of the LED 710D is wire bonded to bondingpad 935; LED 710B (FIG. 7) is disposed on central pad 910 and a contacton the top surface of the LED 710B is wire bonded to bonding pad 930;and LED 710A (FIG. 7) is disposed on central pad 905 and a contact onthe top surface of the LED 710A is wire bonded to bonding pad 925. Inthis embodiment bonding pad 945 serves as a ground. To activate LED 710Ca sufficient voltage is applied to the partial via 965. To activate LEDs710C and 710D a sufficient voltage is applied to the partial via 960. Toactivate all four LEDs 710A-D a sufficient voltage is applied to thepartial via 950. In some embodiments an ESD protection device 975 isconnected between bonding pads 940 and 945.

As in some of the embodiments described above, in further embodimentsthe central pads 905, 910, 915, and 920 are thermal bonding pads and notelectrical bonding pads. In these embodiments, the central pads 905,910, 915, and 920 are not connected by traces to the bonding pads 925,930, 935, and 940 and to the partial via 950, 955, 960, and 965. In someof these embodiments two contacts on LED 710A are wire bonded to bondingpads 940 and 925, LED 710B is wire bonded to bonding pads 925 and 930,LED 710D is wire bonded to bonding pads 930 and 935, and LED 710C iswire bonded to bonding pads 935 and 945. For greater operativeindependence of the LEDs 710A-D bonding pads 925, 930, 935, 940, and 945can be made smaller to accommodate still further bonding pads within theinner diameter 270. These further bonding pads can be electricallyconnected to additional partial vias at the edges of the LED package 700(FIG. 7). It will be appreciated that in those embodiments in which thebonding pads for bonding the LED dice are not electrically conductive,the bonding pads can be merely regions on the floor of the cavity ratherthan a patterned layer of some material on the floor of the cavity. Inother words, the die attach layer 245 bonds the LED dice directly to thefloor of the cavity in the bonding pad region.

FIG. 10 illustrates an exemplary metallization pattern for a bottomsurface of the thermal conduction layer 900 of the LED package 700 ofFIG. 7. This metallization pattern can be used where the bottom surfaceof the LED package 700 is used to make electrical connections to asubstrate, for example, with an array of solder balls. Thus, forexample, each of the partial vias 950, 955, 960, 965, and 970 connect tocontacts 1000, 1005, 1010, 1015, and 1020. An additional central contact1025 helps improve thermal contact with the substrate. The centralcontact 1025 optionally can also serve as an electrical contact. Inthese embodiments, a small patch 1030 of AlN, or another material, canbe placed over the trace 1035 between the central contact 1025 and thepartial via 950 to prevent solder from flowing along the trace 1035during soldering.

In other embodiments, as shown in FIG. 11, the partial vias 950, 955,960, 965, and 970 are electrically connected to contacts 1100, 1105,1110, 1115, and 1120 on a top surface of a top body layer 1125 of theLED package 700 (FIG. 7). In these embodiments, the contacts 1100, 1105,1110, 1115, and 1120 are mounted to bonding pads on a flexible circuitboard. In these embodiments, the bottom of the package is free ofbonding pads and is used for thermal path only. These arrangementssignificantly improve thermal performance for small packages.

3. Method of Fabrication

Methods are disclosed for fabricating a layered LED package as describedwith reference to FIGS. 2-7. The methods vary depending upon thematerials selected for each layer, specific designs, such as the patternof metallization and the location and routing of the electricalconnections, and applications of the LED package. In those embodimentsshown in FIGS. 2-5 and in which all three layers 210, 220, and 230 aremade of a ceramic, for example, the layers 210, 220, and 230 can bemanufactured separately, stacked together, and co-fired (sintered) tobond the layers 210, 220, and 230 together. When non-ceramic materialsare used for layers 210 and 220, however, the layers 210 and 220 can bebonded together with suitable adhesives or solders.

In one embodiment of the method of the invention, multiple LED packagesare formed together in a batch process in which the individual LEDpackages are fabricated in parallel as a panel 800 from which individualLED packages can later be separated. FIG. 8 shows a top view of aplurality of LED packages 810 manufactured in parallel during anexemplary embodiment of a fabrication process. In this embodiment, theLED packages 810, which can be fabricated to include LED dies 820, areassembled in a square grid pattern separated by snap lines 830. Rows orcolumns of the packages 810 can be snapped apart along the snap lines830, and then further sub-divided into individual LED packages 810.According to this embodiment, each of the top body layer (e.g., 210),the intermediate body layer (e.g., 220) and the thermally conductinglayer (e.g. 230) for the plurality of LED packages 810 is produced as awhole piece, and each layer is independently fabricated as a sheet andthen bonded together. LED dies 820 can be added to the grid of LEDpackages 810 before the grid is separated into individual LED packages810.

Easily fractured materials, such as ceramics, are particularly suitedfor the above described embodiment. Separating the grid into theindividual LED packages 810 would be difficult if a metal, such ascopper, is used to form a bottom plate for heat dissipation. If amaterial that is not easily fractured is used for any of the threelayers (e.g., the top body layer 210, the intermediate body layer 220and the thermal conduction layer 230), it may be necessary to preparesuch layers along the snap lines 830 with deep grooves or perforationsto facilitate separation.

The grid in FIG. 8 also includes an array of vias (holes) 840 along thesnap lines 830. Each via 840 is shared by four neighboring LED packages810, except for those located at an edge or corner which would be sharedby either one or two neighboring LED packages 810. After the individualLED packages 810 are separated along the snap lines 830, the vias 840are separated apart to become partial vias (e.g., 290, 292, 294 and296).

To produce a thermally conducting layer (e.g., 230 or 630) using aceramic material according to a particular embodiment, for example, aceramic layer of a material such as AlN is prepared with a square arrayof vias 840 disposed therethrough. The vias 840 sit at the intersectionsof the snap lines 830 in FIG. 8. Ultimately, when the LED packages 810are separated from one another, each via 840 becomes a partial via(e.g., 290, 292, 294, and 296) of four different neighboring packages810. The top and bottom surfaces of the ceramic layer are patterned, inexemplary embodiments, with metallization as shown in FIGS. 4 and 5.Patterning can be achieved, for example, by plating. Suitable metals forthe metallization include tungsten and nickel. These patterns arerepeated for each package 810 that will be produced.

Various patterns of metallization may be used to achieve differenteffects and to suit the different requirements of the LED dies 820. Insome embodiments, for example, the central pad (e.g., the central pad410 in FIG. 5) serves both as a thermal contact and an electricalcontact. In these embodiments, the central pad on the top surface of thethermally conducting layer (230) is connected by a trace (420) to one ofthe partial vias (294) so that an electrical connection extends from thecentral pad to the opposite surface of the thermally conducting layer.If desirable, the electrical connection may be further extended to thecentral pad (510). In these embodiments, a small patch of AlN, oranother material, can be placed over the trace (420) between the centralpad and the partial via to prevent solder from flowing along the traceduring soldering.

To produce an intermediate body layer (e.g., layer 220), according tothis embodiment, a layer of a material such as AlN is prepared with asquare array of vias disposed therethrough. The square array of viasmatches the square array of vias in the thermally conducting layer.Additionally, a square array of apertures is defined in the layer suchthat each aperture is centered in a square defined by four adjacentvias. These apertures correspond to the inner diameter of the cavity(e.g., the inner diameter 270 in FIGS. 2-5) of the respective LEDpackage.

To produce a top body layer (e.g., layer 210), according to thisembodiment, a layer of a material such as AlN is prepared with a squarearray of vias disposed therethrough. The square array of vias matchesthe square arrays in the thermally conducting layer and the intermediatebody layer. Additionally, a square array of apertures is defined in thelayer such that each aperture is centered in a square defined by fouradjacent vias. The array of apertures on the top body layer match thearray of apertures on the intermediate body layer but have a differentdiameter. These apertures are preferably inclined or otherwise shaped toprovide a sidewall as discussed above with respect to FIGS. 1-3.Specifically, in a preferred embodiment, each inclined aperture has atop rim that corresponds to the outer diameter (e.g., the outer diameter260 in FIGS. 2-5) of the cavity in the respective LED package, and abottom rim that corresponds to the inner diameter (e.g., the innerdiameter 270 in FIGS. 2-5) of the cavity in the respective LED package810. The top body layer is then metallized to provide sidewallmetallization and any electrical contacts for the top surface. For theembodiments that do not require electrical contacts for the top surfaceof the top body layer, no electrical contacts are formed on the topsurface.

Once the thermally conducting layer, the intermediate layer and the topbody layer are individually prepared, the three layers are broughttogether in an assembly, the vias in each layer are aligned, and thethree layers are bonded together. As noted above, where all three layersare ceramic the assembly can be co-fired, else the layers can be bondedtogether with a suitable adhesive or solder. In the latter embodiments,the adhesive can serve to electrically insulate the metallization on thetop surface of the thermally conducting layer (e.g., metallizationpattern shown in FIG. 4A) from an intermediate layer comprising a metalsuch as copper. Once the layers have been bonded to one another, thevias 840 can be plated to provide electrical connections betweenmetallizations on the various surfaces of the layers.

Although the LED packages 810 can be separated at this point forsubsequent fabrication into light emitting devices, it is oftendesirable to first attach LED dies 820 to form an entire panel 800 oflight emitting devices in parallel. To create a panel 800 of lightemitting devices, solder flux or a thermally conductive die-attach isdispensed and the LED dies 820 are bonded to the LED packages 810. Then,each LED die 820 is wire bonded to the appropriate bonding pads.Preferably, the cavities of the LED packages 810 are next filled toencapsulate the LED dies 820. In some embodiments this process includesforming a thermally insulating layer over the LED die 820, forming aluminescent layer over the thermally insulating layer, and then forminga lens over the luminescent layer. Finally, the assembly is diced alongthe snap lines 830. It will be appreciated that the light emittingdevices of the present invention can be manufactured with fewerprocessing steps than prior art devices, in some instances fewer thanhalf as many steps.

To produce an embodiment such as that shown in FIG. 6C, in which aceramic alignment layer 695 is included, the method described above canbe modified so that the alignment layer 695 is co-fired together withthe thermally conducting, intermediate, and top body layers.Alternately, a metal alignment layer 695 can be bonded to the top bodylayer with a suitable adhesive or solder.

In those embodiments that include an alignment mechanism for aligning alens such as lens 690 in FIGS. 6B and 6C, the lens can be added to thepackage 810 in a number of different ways. In some embodiments, a vacuumtool is used to pick up a lens and move the lens into position. In otherembodiments a number of lenses are held on a strip of tape; a lens onthe tape is aligned with the package 810 and a tool presses the lensinto the guide to transfer the lens from the tape and to the package810. It will be appreciated that lens transfer by vacuum tool or fromtape can be achieved either before or after the LED packages 810 areseparated from one another.

In an exemplary batch process that can be performed before the LEDpackages 810 are separated from the panel 800, the lenses are formed byinjection molding. In this process a mold having an array of lens-shapedwells is sealed to the panel 800 so that one well is aligned with eachof the packages 810. A suitable plastic is injected into the mold tofill the wells. The plastic is then cured to form the lenses. In anotherexemplary batch process, the lenses are formed by mask printing.

In the foregoing specification, the present invention is described withreference to specific embodiments thereof, but those skilled in the artwill recognize that the present disclosure is not limited thereto.Various features and aspects of the above-described invention may beused individually or jointly. Further, the present invention can beutilized in any number of environments and applications beyond thosedescribed herein without departing from the broader spirit and scope ofthe specification. The specification and drawings are, accordingly, tobe regarded as illustrative rather than restrictive, It will berecognized that the terms “comprising,” “including,” and “having,” asused herein, are specifically intended to be read as open-ended terms ofart. It will be further recognized that “LED” and “LED die” are usedinterchangeably herein.

1. A package for multiple LEDs comprising: a body including top andbottom surfaces; a cavity extending from the top surface towards thebottom surface and having a floor that is substantially parallel to thebottom surface; a thermally conducting material disposed between thefloor and the bottom surface; a plurality of LED bonding pads disposedon the floor; and a plurality of electrical bonding pads disposed on thefloor proximate to the LED bonding pads and in electrical communicationwith a plurality of electrical contacts disposed on a surface of thebody, the plurality of electrical bonding pads in electricalcommunication with the plurality of electrical contacts through aplurality of vias and at least one of the plurality of vias consistingof a partial via.
 2. The package of claim 1 wherein the thermallyconducting material comprises a ceramic.
 3. The package of claim 1wherein the plurality of electrical contacts are disposed on the bottomsurface of the body.
 4. The package of claim 1 further comprising an ESDprotection device coupled between two of the plurality of electricalbonding pads.
 5. A package for multiple LED's and for attachment to asubstrate comprising: a top body layer; a cavity disposed through thetop body layer and having a floor for bonding to the multiple LED's; athermal conduction layer bonded to the top body layer and having a topsurface forming the floor of the cavity and a bottom surface, thethermal conduction layer including a thermally conducting ceramicmaterial disposed between the floor and the bottom surface; a pluralityof LED bonding pads in direct contact with the floor and configured tobond to the multiple LED's; and a plurality of electrical bonding padsin direct contact with the floor, proximate to the LED bonding pads, andin electrical communication with a plurality of electrical contactsdisposed on a surface of the body.
 6. The package of claim 5 furthercomprising a central pad disposed on the bottom surface of the thermalconduction layer and having a continuously curved periphery without acorner.
 7. The package of claim 6 wherein at least one of the electricalcontacts is in electrical communication with the central pad.
 8. Thepackage of claim 5 wherein the plurality of electrical contacts aredisposed on the bottom surface of the thermal conduction layer.
 9. Thepackage of claim 5 further comprising a luminescent layer disposed overthe LED dies and a thermal insulation layer disposed between theluminescent layer and the LED dies.
 10. The package of claim 5 furthercomprising a via configured to provide electrical communication betweenat least one of electrical bonding pads and at least one of theplurality of electrical contacts wherein the via consists of a partialvia.
 11. The light emitting device of claim 5 wherein the plurality ofLED bonding pads are electrically conductive.